Field of the Invention
Embodiments of the invention generally relate to an end effector configured to transfer a substrate, more specifically, for an end effector configured to transfer a thin substrate using an electrostatic chucking force.
Description of the Related Art
Ultra-large-scale integrated (ULSI) circuits may include more than one million electronic devices (e.g., transistors) that are formed on a semiconductor substrate, such as a silicon (Si) substrate, and cooperate to perform various functions within the device. Typically, the transistors used in the ULSI circuits are complementary metal-oxide-semiconductor (CMOS) field effect transistors. A CMOS transistor has a gate structure comprising a polysilicon gate electrode and gate dielectric, and is disposed between a source region and drain regions that are formed in the substrate.
During manufacture of the integrated circuits, display devices or other semiconductor related products, a number of different chemical and physical processes are involved whereby minute transistor devices are created on a substrate. Layers of materials which make up the transistor devices are created by chemical vapor deposition, physical vapor deposition, epitaxial growth, and the like. Some of the layers of material are patterned using photoresist masks and wet or dry etching techniques. The substrate utilized to form transistor devices may be silicon, quartz, sapphire, gallium arsenide, indium phosphide, glass, or other appropriate material. In some applications, flexible substrates, polymer substrates or plastic substrates may also be utilized.
During processing, the substrate needs to be transferred in between processing tools and chambers. After a number of processes, the substrate may be thinned compared to its original substrate thickness. For example, a portion of the substrate may be grounded or polished away during the processes, thereby resulting thickness loss to the substrate. When a substrate thickness is thinned down to 100 μm or less, it becomes fragile. It has become more challenging in transferring these thin substrates during processes without damaging or fragmenting the substrates. Using a conventional mechanical end effector to clamp a fragile substrate during transfer may often result in substrate damage due to the high mechanical clamping and contact force. Furthermore, for the substrates used for smart phones, LED or solar cell applications, small size substrates are often selected for manufacture. It even increases difficulty in transferring the fragile substrates with small sizes.
In some cases, the substrates may need to be flipped over, e.g., inverted, to process the substrate from their backside, a surface without transistor or devices formed thereon. Examples of these processes include through silicon vias (TSVs), substrate backside grounding, or substrate backside cleaning or scrubbing. In these applications, minimum physical contact for the end effector to be in contact with the substrate is desired so as to avoid contamination or physical damage during substrate contact for transferring. However, conventional mechanical transfer often requires a certain degree of physical contact for the end effector to the substrate so as to ensure a sufficient clamping force applied thereto to securely pick up the substrate. This mechanical contact inevitably creates contact contamination or physical damage, undesirably polluting the substrate.
Therefore, there is a need for an apparatus for transferring thin substrates with minimum contact.